The TETRA (TErrestrial Trunked RAdio) system is a digital mobile communications system developed primarily for public safety and security, for public trunking operators, and for utilities and industry. A typical TETRA network architecture, as illustrated in FIG. 4, comprises digital exchanges DXT_1, DXT_2 (DXT, Digital Exchange for TETRA) to which base stations TBS_1, TBS_2 (TBS, TETRA Base Station) are connected. HLR (Home Location Register) describes for its part a register of the network where all subscriber parameters of mobile subscribers UE1, UE2 (UE, User Equipment) are permanently stored. VLR (Visited Location Register) describes a register of the mobile network where all subscriber parameters for call set-up are stored as long as mobile subscribers UE1, UE2 are in a location area controlled by this register. In TETRA system VLR registers may be located in connection with exchanges. Reference numeral 1-2 describes e.g. a fixed communications network to which the user UE1, UE2 can be connected via one or more exchanges DXT_1, DXT_2.
A base transceiver station (TBS for TETRA) is the mobile's interface to the network. The station is responsible for radio transmission and reception to or from the mobile station, i.e. to provide the air interface between the radio units and Switching and Management Infrastructure SwMI. The base station converts the digital baseband signals to the radio frequency RF and vice versa. The base station may comprise e.g. transceivers and their power supplies, a combiner, a power divider, a ciphering device and amplifiers.
As can be seen from above many different functions has been given to base transceiver stations. In state of the art network configurations has been like star network configurations with base stations as spatially single entities. This has sometimes lead to problems like unequally divided loads between different parts of the network causing e.g. quality of service to deteriorate at times.